This project will continue studies on the contributions of vestibular otolith and semicircular canal inputs to normal and abnormal human balance control, but will be expanded to study visual contributions to postural control sensory interactions. The specific aims are to: 1) determine sources of variability of otolith-vestibulo-ocular reflexes and vestibular evoked myogenic potentials in patients with vestibular deficiencies and in an existing normal population cross-sectioned by age decade and gender, 2) determine otolith and canal contributions to postural control in normals and patients with vestibular deficits, 3) determine the role of altered otolith inputs to adaptive postural control in normal and vestibular deficient subjects, 4) determine the role of macular and peripheral retinal contributions to the sensory interaction controlling posture, and 5) study gait initiation in normals, and patients with vestibular or visual disorders under controlled head and gaze position. Studies will be performed on computer controlled rotation devices and dynamic platform systems. Vestibulo-ocular responses to angular, linear or combined angular and linear accelerations will be used as independent estimates of vestibular function. Eye movement responses will be recorded by conventional electro-oculography and three-dimensional infrared video techniques and analyzed for horizontal, vertical and torsional eye movements, depending on the experiments. Balance, posture and gait responses will be recorded using a forceplate and an active marker motion analysis system and analyzed for torque and force measurements of the feet and for multi-dimensional body movements (head, trunk, legs) using special purpose computer methods. Outcomes of these experiments have resulted and will likely continue to result in a better understanding of normal and abnormal vestibulo-ocular and vestibulo-spinal control mechanisms, and will contribute to the development of new methods of diagnosis, prevention, treatment and rehabilitation of human balance disorders, including falls in the elderly.